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Michigan: Oak wilt past, but wood could infect live trees

 
By KEVIN WALKER
Michigan Correspondent

LANSING, Mich. — The Michigan Department of Natural Resources (DNR) is asking residents not to move oak wilt-infected wood, even though the “infection window” has passed.
July 15 marked the end of the three-month window when oak wilt can be transmitted from diseased to healthy red oak trees this year, the DNR says. Between April 15-July 15 spores, which are produced from oak wilt-killed trees, can infect healthy oak if the tree has been “injured,” said John Pepin, a spokesman for DNR.
“We don’t want you moving the wood now because it contains spores and next year beetles could take the spores and infect healthy trees,” Pepin explained.
An “injured” healthy tree could be one that has been pruned, damaged in a storm or damaged by high winds. Spores that are moved along with the wood can survive the winter and pose a threat to a healthy stand of trees the following year, during the next infection window.
Once the disease infects one tree the disease can be spread through a network of roots. Oaks within 100 feet of each other may have connected or grafted root systems. Left untreated, oak wilt will continue from tree to tree, progressively killing more oak over an increasingly larger area.
Oak wilt is mainly a disease of red oak trees, which includes northern red oak, black oak and pin oak. Red oaks often die within a few weeks of becoming infected. Because white oak is more resistant to oak wilt, the disease progresses more slowly in stands of this.
DNR advises tree owners not to prune or otherwise “injure” oaks during the April 15-July 15 time frame. Sap beetles are attracted to spore pads from oak wilt-killed trees. They carry the spores to wounds on healthy oaks. The beetles are also attracted to oak tree wounds.
Spring is a popular time for people to move firewood to vacation properties in other locations. Oak trees are often cut into firewood and moved, sometimes far from their original locations. Naturally, a dead or damaged tree is seen as a candidate for felling and use as firewood; however, when such wood is brought to a new location healthy oaks there can become infected over time.
According to DNR’s most recent Forest Health Highlights report, oak wilt is one of the most serious tree diseases in the eastern United States, killing thousands of oaks each year in forests, woodlots and home landscapes. Oak wilt was first identified in 1944, but because of the difficulty in isolating and identifying the fungus that causes the disease, recognition of its impact was delayed until the 1980s.
According to the DNR, although other tree diseases may be indistinguishable from oak wilt up to a point, a distinguishing feature of oak wilt is that it causes the tree to suddenly drop its leaves in July or August. In Michigan, the disease is widely established in the southern Lower Peninsula and has spotty distribution in the northern Lower and Upper peninsulas.
“As the public moves northward into forested areas, the risk of spreading this disease grows,” the report stated.
The DNR is hoping to get people to report oak wilt-infected trees. Tree owners should be able to get an infection confirmed by a forester through their local conservation district, Pepin said.
The agency is also asking people to report a suspected oak wilt site by emailing the department at DNR-FRD- Forest-Health@michigan.gov or by calling 517-284-5895.
7/29/2015